1. Field of the Invention
The present invention relates to ducts as used in post-tension construction. More particularly, the present invention relates to the formation of a polymeric duct used for retaining multi-strand tensioning systems within an encapsulated environment.
2. Description of Related Art
For many years, the design of concrete structures imitated the typical steel design of column, girder and beam. With technological advances in structural concrete, however, its own form began to evolve. Concrete has the advantages of lower cost than steel, of not requiring fireproofing, and of its plasticity, a quality that lends itself to free flowing or boldly massive architectural concepts. On the other hand, structural concrete, though quite capable of carrying almost any compressive load, is weak in carrying significant tensile loads. It becomes necessary, therefore, to add steel bars, called reinforcements, to concrete, thus allowing the concrete to carry the compressive forces and the steel to carry the tensile forces.
Structures of reinforced concrete maybe constructed with load-bearing walls, but this method does not use the full potentialities of the concrete. The skeleton frame, in which the floors and roofs rest directly on exterior and interior reinforced-concrete columns, has proven to be most economic and popular. Reinforced-concrete framing is seemingly a quite simple form of construction. First, wood or steel forms are constructed in the sizes, positions, and shapes called for by engineering and design requirements. The steel reinforcing is then placed and held in position by wires at its intersections. Devices known as chairs and spacers are used to keep the reinforcing bars apart and raised off the form work. The size and number of the steel bars depends completely upon the imposed loads and the need to transfer these loads evenly throughout the building and down to the foundation. After the reinforcing is set in place, the concrete, a mixture of water, cement, sand, and stone or aggregate, of proportions calculated to produce the required strength, is placed, care being taken to prevent voids or honeycombs.
One of the simplest designs in concrete frames is the beam-and-slab. This system follows ordinary steel design that uses concrete beams that are cast integrally with the floor slabs. The beam-and-slab system is often used in apartment buildings and other structures where the beams are not visually objectionable and can be hidden. The reinforcement is simple and the forms for casting can be utilized over and over for the same shape. The system, therefore, produces an economically viable structure. With the development of flat-slab construction, exposed beams can be eliminated. In this system, reinforcing bars are projected at right angles and in two directions from every column supporting flat slabs spanning twelve or fifteen feet in both directions.
Reinforced concrete reaches its highest potentialities when it is used in pre-stressed or post-tensioned members. Spans as great as one hundred feet can be attained in members as deep as three feet for roof loads. The basic principle is simple. In pre-stressing, reinforcing rods of high tensile strength wires are stretched to a certain determined limit and then high-strength concrete is placed around them. When the concrete has set, it holds the steel in a tight grip, preventing slippage or sagging. Post-tensioning follows the same principle, but the reinforcing tendon, usually a steel cable, is held loosely in place while the concrete is placed around it. The reinforcing tendon is then stretched by hydraulic jacks and securely anchored into place. Pre-stressing is done with individual members in the shop and post-tensioning as part of the structure on the site.
In a typical tendon tensioning anchor assembly used in such post-tensioning operations, there are provided anchors for anchoring the ends of the cables suspended therebetween. In the course of tensioning the cable in a concrete structure, a hydraulic jack or the like is releasably attached to one of the exposed ends of each cable for applying a predetermined amount of tension to the tendon, which extends through the anchor. When the desired amount of tension is applied to the cable, wedges, threaded nuts, or the like, are used to capture the cable at the anchor plate and, as the jack is removed from the tendon, to prevent its relaxation and hold it in its stressed condition.
Multi-strand tensioning is used when forming especially long post-tensioned concrete structures, or those which must carry especially heavy loads, such as elongated concrete beams for buildings, bridges, highway overpasses, etc. Multiple axially aligned strands of cable are used in order to achieve the required compressive forces for offsetting the anticipated loads. Special multi-strand anchors are utilized, with ports for the desired number of tensioning cables. Individual cables are then strung between the anchors, tensioned and locked as described above for the conventional monofilament post-tensioning system.
As with monofilament installations, it is highly desirable to protect the tensioned steel cables from corrosive elements, such as de-icing chemicals, sea water, brackish water, and even rain water which could enter through cracks or pores in the concrete and eventually cause corrosion and loss of tension of the cables. In multi-strand applications, the cables typically are protected against exposure to corrosive elements by surrounding them with a metal duct or, more recently, with a flexible duct made of an impermeable material, such as plastic. The protective duct extends between the anchors and in surrounding relationship to the bundle of tensioning cables. Flexible duct, which typically is provided in 20 to 40 foot sections is sealed at each end to an anchor and between adjacent sections of duct to provide a water-tight channel. Grout then may be pumped into the interior of the duct in surrounding relationship to the cables to provide further protection.
Various patents have issued, in the past, for devices relating to such multi-strand duct assemblies. For example, U.S. Design Pat. No. 400,670, issued on Nov. 3, 1998, to the present inventor, shows a design of a duct. This duct design includes a tubular body with a plurality of corrugations extending outwardly therefrom. This tubular duct is presently manufactured and sold by General Technologies, Inc. of Stafford, Tex., the licensee of the present inventor. In particular, FIGS. 1 and 2 are illustrations of the prior art duct that is being manufactured by General Technologies, Inc.
As can be seen in FIG. 1, the tubular duct 10 has a tubular body 12 and a plurality of corrugations 14 which extend radially outwardly from the outer wall 16 of the tubular body 12. The tubular body 12 includes an interior passageway 14 suitable for receiving multiple post-tension cables and strands therein. The interior passageway 18 of the tubular body 12 is suitable for receiving a grout material so as to maintain the multiple strands in a liquid-tight environment therein. FIG. 2 shows the tubular body 12 as having the corrugations 14 extending outwardly in generally spaced parallel relationship to each other and in transverse relationship to the longitudinal axis of the tubular body 12. A wall 16 will extend between the corrugations 14. The tubular body 12, along with the corrugations 16, are formed of a polymeric material. The duct 12 can be any length, as desired. Couplers can be used so as to secure lengths of duct 10 together in end-to-end relationship.
One of the problems associated with the prior art duct 10 is that it is not stiff enough in the longitudinal direction. The duct 10 will flex too easily. It becomes difficult to profile such an easily flexible duct. When the cables are being installed in the interior passageway 18, the cablepusher used to install the cable within the interior passageway 18 is likely to strike the walls of the interior passageway 18 when the duct is flexed. Because of the force used to install the cable through the duct 10, the walls of the duct can break or become damaged if the cable strikes the walls of the duct. It is desirable to manufacture a duct 10 with greater stiffness and rigidity in the longitudinal direction so as to avoid the flexing and deflection of the duct.
An additional problem with the duct 10, as shown in FIGS. 1 and 2, is that air has a possibility of being trapped in the corrugations. When air bubbles form within the interior of the corrugations, the grout used to seal the interior 18 does not effectively encapsulate the cable on the interior 18. As such, it is desirable to manufacture the duct 10 such that the potential for trapped air bubbles within the corrugations 14 is reduced.
The present inventor is also the inventor of U.S. Pat. No. 5,474,335, issued on Dec. 12, 1995. This patent describes a duct coupler for joining and sealing between adjacent sections of duct. The coupler includes a body and a flexible cantilevered section on the end of the body. This flexible cantilevered section is adapted to pass over annular protrusions on the duct. Locking rings are used to lock the flexible cantilevered sections into position so as to lock the coupler onto the duct. U.S. Pat. No. 5,762,300, issued on Jun. 9, 1998, to the present inventor, describes a tendon-receiving duct support apparatus. This duct support apparatus is used for supporting a tendon-receiving duct. This support apparatus includes a cradle for receiving an exterior surface of a duct therein and a clamp connected to the cradle and extending therebelow for attachment to an underlying object. The cradle is a generally U-shaped member having a length greater than a width of the underlying object received by the clamp. The cradle and the clamp are integrally formed together of a polymeric material. The underlying object to which the clamp is connected is a chair or a rebar.
U.S. Pat. No. 5,954,373, issued on Sep. 21, 1999, to the present inventor, shows another duct coupler apparatus for use with ducts on a multi-strand post-tensioning system. The coupler includes a tubular body with an interior passageway between a first open end and a second open end. A shoulder is formed within the tubular body between the open ends. A seal is connected to the shoulder so as to form a liquid-tight seal with a duct received within one of the open ends. A compression device is hingedly connected to the tubular body for urging the duct into compressive contact with the seal. The compression device has a portion extending exterior of the tubular body.
It is an object of the present invention to provide a tendon-receiving duct which improves the rigidity of the duct in the longitudinal direction.
It is another object of the present invention to provide a tendon-receiving duct which facilitates the removal of air bubbles within the interior of the duct.
It is a further object of the present invention to provide a tendon-receiving duct apparatus which facilitates the ability to install the cable within the duct.
It is still a further object of the present invention to provide a tendon-receiving duct which is easy to manufacture, easy to use, and relatively inexpensive,
These and other objects and advantages of the present invention will become apparent from a reading of the attached specification and appended claims.
The present invention is a tendon-receiving duct comprising a tubular body having a longitudinal axis. The tubular body has a plurality of corrugations extending radially outwardly therefrom. Each of the plurality of corrugations is in spaced relationship to an adjacent corrugation. The tubular body has an interior passageway suitable for receiving tendons therein. Each of the plurality of corrugations opens to the interior passageway. The tubular body has a longitudinal channel extending between adjacent pairs of plurality of corrugations.
In the present invention, the tubular body has a wall extending between the adjacent pair of corrugations. The longitudinal channel extends outwardly of this wall. The longitudinal channel has an interior which opens to the interior passageway of the tubular body. The longitudinal channel also has one end which opens to one of the pairs of corrugations and at an opposite end which opens to the other of the pair of corrugations. A plurality of longitudinal channels extend around the tubular body between the adjacent pair of corrugations. Each of the plurality of longitudinal channels is spaced by an equal radial distance from an adjacent longitudinal channel.
The plurality of corrugations can be connected together in fluid communication by the longitudinal channel. The longitudinal channel extends to each of the plurality of corrugations. The longitudinal channel will extending outwardly of the tubular body by a distance equal to the distance that the plurality of corrugations extend outwardly of the tubular body.
In one embodiment of the present invention, the tubular body has a circular cross-section in a plane transverse to the longitudinal axis of the tubular body. In another embodiment of the present invention, the tubular body has an oval cross-section in a plane transverse to a longitudinal axis of the tubular body.
The present invention can further comprise a plurality of tendons which extend through the interior passageway of the tubular body, and a grout material which fills the interior passageway of the tubular body. The grout material fills the plurality of corrugations and the longitudinal channel.